Microwave guide rotatable joint



Feb. 19, 1957 J. F. ZALESKl MICROWAVE GUIDE ROTATABLE JOINT Filed April 27, 1954 2 M\ v a INVENTOR. r/UHNEZ 9LE5K/ BY 3/ 34% fiTTO/Q/VEY.

2 ,782,384 lC Patented Feb- 19, 1957 MICROWAVE GUIDE ROTATABLE JOINT John F. Valeski, Valhalla, N. Y., assignor to General Precision Laboratory Incorporated, a corporation of New York Application April 27, 1954, Serial No. 425,810

11 Claims. (Cl. 333-98) This invention relates to rotatable joints in microwave guides.

in applying microwave energy to rotating or oscillating apparatus, such as scanning antennas, it becomes necessary to transfer the energy from a fixed transmitting guide to a rotating guide. The present invention accomplishes this with input and output guides in axial alignment and without resorting to the use of transmission in a radially symmetrical mode. The manner of accomplishment in cludes the energization of a round hollow guide in the T511 or some other polarized mode, employment in the round guide of an adjustable .polarity rotating device, and the use of means controlled by the desired output rotation angle for adjusting the polarity-rotating device.

One convenient polarity-rotating device depends upon the peculiar property of certain substances, when magnetizcd, of changing the angle of polarization of microwave electromagnetic field energy impinging on them, the amount of change being dependent upon the degree of magnetization. Accordingly such a polarity-changing device can be employed in a preferred embodiment of the instant invention which is, however, by no means restricted to the use of this species of polarity-rotating device.

The principal purpose of this invention is to provide a microwave rotatable joint having a mechanical rotatable joint and a field polarity rotating device acting in concert.

Another purpose of this invention is to provide a round hollow guide containing a device for changing the polarization direction of microwave energy passing through it, in combination with a mechanical rotatable connection.

Another purpose of this invention is to provide a microwave rotatable joint having a rotatable mechanical connection between two round hollow guides, a polarityrotating device in one of the guides and a variable resistance operated by the mechanical connection to control the polarity-rotating device.

A further understanding of this invention may be secured from the detailed description and associated drawings, in which:

igure 1 is an external view of a microwave guide rotatable joint embodying the invention.

Figure 2 is a cross section of a polarity-rotating device for rota-ting a microwave field.

Figures 3, 4 and 5 are circuits for use with the rotatable joint of Fig. 1.

Referring now to Fig. l, a rectangular guide 11 for transmission of microwave energy in the T1310 mode of a selected frequency band is connected to a round microwave guide assembly 12, for transmission of microwave energy'of the same frequency band in the TEu mode. An appropriate matching device such as an iris is employed if necessary between guide 11 and assembly 12 to eliminate i pedance discontinuity. The round guide assembly 12 is continued through choke flange 13 and round guide section 14 to the mechanical rotating joint 16 which connects the guide 14 to a similar short round guide 17. The mechanical rotating joint 16 is of conventional design and may contain an annular choke recess to prevent leakage of microwave field and a packed joint to permit use in a pressurized system. The short round guide is connected to a rectangular guide 18 employing an appropriate impedance matching device such as an iris. This guide 18 also is of the proper size for transmission of the same frequency band in the TElO mode.

Although rectangular guide is commonly used for microwave transmission and is shown employed in Fig. 1, any other type of guide may of course be employed to lead microwave energy into and out of the microwave rotatable joint of the invention. The invention is not restricted to the use of round hollow guide in the microwave rotatable joint, but round dielectric guide or any other circular guide may be employed instead.

The round guide assembly section 12 incorporates a device active in the Faraday magneto-optical sense for rotating the plane of polarization of microwave energy passed through it. One example of such a device is generally described in Patent No. 2,644,930, issued July 7, 1953, and makes use of the polarizing property of a magnetized rod of selected material. This device includes the round metallic microwave guide 19, Fig. 2, provided with connection flanges 21 and 13. A coil 22 having two end terminals 23 and 24 is wound around the outside of guide 19. The interior of the guide 19 is completely filled with a solid low-loss dielectric material 26 such as tetrafiuoroethylene except for an axial space occupied by a rod 27. This rod is composed of a comminuted material which is active in the Faraday magnetooptical sense. One such rod material, known as Ferramic D, may be obtained from the General Ceramics and Steatite Corp, Keasbey, New Jersey. The diameter of the round guide 19 and the properties of the dielectric 26 are so chosen that the device can be secured by its flanges to conventional sizes of rectangular or round hollow guide without the use of matching elements.

The round guide section 14, Fig. 1, is surrounded by a helix of resistance wire 23 having one or more terminals, and being either continuous around the periphery of the round guide or discontinuous, in accordance with circuit requirements. One or two or more brushes bear on the resistance wire 28 and making sliding contact with it, two such brushes 29 and 31 together with their indicated brush structures 2i and 31 being shown in diametrically opposite positions in the figure. The brush structures 29 and 31 are secured to the short guide 17 but are electrically insulated therefrom by insulating sheets 32 and 33. Since the resistance coil 28 and the brushes are secured on opposite sides of the rotatable joint 16, any joint rotation causes the brushes to slide along the resistance wire. The same relative motion and brush action would be secured if the resistance coil 28 were secured to guide 17 and the brushes to guide 14.

The invention can be used to perform several different functions, and the circuits including the coil 22 and the resistance wire 28 differ in the several cases. if, for example, it is desired to supply microwave energy to an oscillating scanning antenna having an angular scan of on each side of its central position, the circuit of Fig. 3 may be employed.

In this figure the circular resistance 34 represents resistor 28, Fig. 1, and is provided with two terminals 36 and 37. A direct-current potential source 38 is connected to these terminals 36 and 37 so that there is a continuous linear fall of potential in each of the two branches of resistance 34. Two diametrically opposite sliders 39 and 40 are connected to coil 22 representing the coil winding 22, Fig. 2, of the polarity-rotating device. The microwave energy may be applied either to rectangular guide 11, Fig. l, or to guide 18, as desired, but the direction of current flow in the polarity-rotating device coil must be appropriate. Let it be supposed that microwave energy at a frequency of 8800 me. p. s. be applied to rectangular guide 11 as an input, and that the energy leaves guide 18 to enter a transmitting antenna. The antenna together with guide 18 and the short round guide 17 are scanned or oscillated through an arc of i90, by means not shown, around an axis which is also the axis of the rotatable joint 16. The round guide 14 and other components on that side of the rotatable joint 16 are fixed in position, while the components on the right side of the rotatable joint 16 oscillate with the antenna. It follows that the two brushes and 31 move on resistance coil 28 through i90 arcs. Their motion is represented in Fig. 3 by the movement of brush 39 on the left branch of resistance 34 between terminals 36 and 37, and by the movement in opposite sense of the other brush 40.

In operation, when brush 39 is at a and brush 48 is at b, no current flows in coil 22 and the polarity-rotating device does not change the polarization of the microwave field passing through it. This condition corresponds to the antenna position in which guides 11 and 18 are collinear, element for element, as depicted in Fig. 1. In this situation the field from guide 11 excites the TEn mode in the round guide 12, with central voltage lines parallel, and this orientation of the field persists through guides 14 and 17 so that it excites the T1310 mode in guide 18 without loss, since the central voltage lines are parallel. If now the antenna rotates the brushes assume the 45 position depicted in Fig. 3 and coil 22 is energized. This produces in the structure of Fig. 2 longitudinal magnetic flux through rod 27, which in turn afiects the transverse electric microwave field passing through guide 19 in such manner as to change the direction of polarization of the field. The direction and amount of polarization change are so designed as to be equal to the direction and amount of antenna angular motion, with the result that the field polarization as it leaves the short round guide 17 is exactly correct to enter the rectangular guide 18, and without loss fully excites the TEio field mode therein. Upon continuance of the antenna motion to the 90 point, when brush 39, Fig. 3, is at terminal 36 and brush 40 is at terminal 37, the field is further rotated so that it still enters guide 18 without loss. Upon return of the antenna to the opposite extreme of its oscillatory motion, brush 39 is moved through position a to terminal 37 and brush 419 to terminal 36. This reverses the current through coil 22, reversing the direction of polarization change of the polarity rotating device, maintaining at all angular positions the proper relation of the field polarity to the position of the output guide 18.

Another use for this invention is to feed an antenna which rotates continuously in one direction. The circuit of Fig. 3 is inadequate in this case and the circuit of Fig. 4 may be employed. This circuit quickly changes the coil energization from minimum to maximum, or vice versa, without hiatus, then slowly changes the coil energization throughout 180. It is necessary in this case always to excite the coil with current in one selected direction, and it is also necessary for the rotating device to be capable at maximum excitation of rotating the field 180. The helix 28, Fig. 1, is broken into two semicircular sections, 41 and 42, Fig. 4, each with two terminals 43, 44, 46, and 47, and a single brush 48 is required. The coil 22 is connected between a tenninal, such as terminal. 43, and the brush 48. Terminals 43 and 47 are strapped together and terminals 44 and 4e are strapped together. A battery 49, with a series resistor 51 to prevent destructive short-circuit effects when the brush passes from one resistor to another, is connected between terminals 46 and 47.

In operation, commencing with the brush 48 at terminal 43 and with input and output rectangular guides 11 and 18 collinear, the coil current is zero, the field is not rotated and passes correctly into the output rectangular guide 18. As the antenna and output guide 18 turn, the brush 48 is rotated counterclockwise in the figure and the coil 22 is energized to rotate the field in such direction and at such rate as to continue to pass into the output guide 18 at its correct orientation. This continues for 180. At this point the brush leaves the resistor 41 at terminal 44 and the current in coil 22 falls to zero, causing the field to reverse 180. The field, however, is still in correct orientation to enter the output guide because of the bisymmetry of its field mode. Since the current tlow in coil 22 is zero after the brush makes contact with resistor 42 at terminal 47, a momentary loss of contact in going from terminal 44 to terminal 47 causes no break in the continuous correspondence of the electric field direction with the E-vector direction of the output guide. Also, if when the brush in passing from terminal 44 to terminal 47 momentarily short-circuits them, no break in the proper matching of the field to the output rectangular guide occurs because of the series resistor 51. This resistor absorbs all of the potential drop of battery 49 while terminals 44 and 47 are shortcircuited, so that no current flows in coil 22 during this instant. For the same reasons no hiatus occurs when brush movement is in the opposite direction, from terminal 47 to terminal 44.

A modification of the circuit is illustrated in Fig. 5. This modification has the advantage of reducing by onehalf the maximum current requirement of the coil by applying current varying from a maximum value through zero to an equal maximum value in the opposite sense. This circuit is applicable to a component as described in connection with Fig. 2, in which the microwave energy in the round guide is in the "FEM mode.

In this modification the helix 23, Fig. 1, is composed of two semicircular sections, 41 and 42, Fig. 5, each with two terminals 43, 44, 46 and 47, and a single brush 48 is arranged to rotate upon them, passing from the end terminal of one semicircular section to an end terminal of the other semicircular section without breaking circuit continuity but with momentary short-circuit of the two terminals. Terminals 43 and 47 are strapped together and terminals 44 and 46 are strapped together. A direct current source consists of two approximately equal battery sections 52 and 53 joined at a midterminal 54. The coil winding 22 is connected between the brush 48 and the midterminal 54.

In the operation of this device the brush 48 is continuously rotated counterclockwise, causing the current in coil 22 to pass from a positive maximum value through zero to an approximately equal negative maximum value, then jumping as the brush passes from one terminal to the other to the maximum positive value. The coil is so constructed that it concomitantly changes the microwave polarization through 180, or more accurately from through zero to +90, then jumping back to -90". The brush in passing from one terminal to the other does not break contact, and in short-circuiting the terminals causes no hiatus in excitation of the coil because of a resistor 56 inserted in one side of the battery connections. When, for example, the brush passes from connection with terminal 46 to connection with both terminals 46 and 43, the entire battery potential is consumed in resistor 56 and the potential efiective at the brush is therefore that of battery terminal 52. The brush potential thus passes instantly from that of terminal 53 to that of terminal 52'.

What is claimed is:

1. A microwave rotatable joint comprising, a first circular waveguide section, a second circular waveguide section, a rotatable joint connecting said first .and second circular waveguide sections, means for passing microwave field energy in a mode having full-period circumferential variation of intensity through said waveguide sections, a member active in the Faraday magneto-optical sense positioned in said first circular waveguide section,

and electromagnetic coil on said first circular waveguide section positioned to impress a magnetic field on said member, an annular resistor positioned around one of said waveguide sections, brush means anchored on the other of said waveguide sections slidably engaging said resistor at positions determined by the angular relation of said first and secondwaveguide sections, a direct current source connected to said resistor to produce a potential drop therein and circuit means interconnecting said brush means and said coil for controlling the sense and amplitude of direct current applied to said coil through said resistor to adjust the sense and degree of microwave field rotation produced by the interaction of said magnetic field on said member to equal the sense and degree of relative rotation of the first and second waveguide sections.

2. A microwave rotatable joint adapted to be energized by microwave energy in a non-circular mode comprising, a pair of circular waveguide sections interconnected by a rotatable joint, an elongated member active in the Faraday magneto-optical sense positioned interiorly of one of said wave guide sections, an electromagnetic coil positioned to impress a magnetic field on said member longitudinally thereof, an annular resistor encircling one of said waveguide sections, contact means aflixed to the other of said waveguide sections slidably engaging said resistor, a direct current source connected to spaced terminals on said resistor producing a potential drop therein, and circuit means interconnecting said contact means and said coil whereby the magnetic field produced by said coil is adjusted by such an amount that the interaction thereof with said member rotates the energy field in said waveguide sections through an angle equal to the relative angular displacement of said waveguide sections.

3. A microwave rotatable joint adapted to be energized by microwave energy in the TE11 mode comprising, a pair of circular waveguide sections interconnected by a rotatable joint, an elongated member active in the Faraday magneto-optical sense positioned interiorly of one of said waveguide sections, an electromagnetic coil positioned to impress a magnetic field on said member longitudinally thereof, a continuous annular resistor sur-- rounding one of said waveguide sections, a pair of contacts afiixed to the other of said waveguide sections and slidably engaging said resistor at diametrically opposed points, said point of engagement being determined by V the relative angular adjustment of said waveguide sections, a direct current source connected to diametrically opposed terminals on said resistor, and a circuit connecting opposite end terminals of said coil to respective ones of said pair of contacts.

4. A microwave rotatable joint adapted to be energized by microwave energy in the TE11 mode comprising, a pair of circular waveguide sections interconnected by a rotatable joint, an elongated member active in the Faraday magneto-optical sense positioned interiorly of one of said waveguide sections, an electromagnetic coil positioned to impress a magnetic field on said member longitudinally thereof, a direct current source, a pair of semicircular resistors encircling one of said waveguide sections, said resistors being connected in parallel with each other and said source, a contact member afiixed to the other of said waveguide sections and slidably engaging a one or the other of said pair of resistors at a point determined by the relative angular adjustment of said waveguide sections, and circuit means connecting said coil between said contact and a terminal of said direct current source.

5. A microwave rotatable joint adapted to be energized by microwave energy in the TE11 mode comprising, a pair of circular waveguide sections interconnected by a rotatable joint, an elongated member active in the Faraday magneto-optical sense positioned interiorly of one of said waveguide sections, an electromagnetic coil speaker positioned to impress a magnetic field on said member longitudinally thereof, a direct current source, a pair of. semicircular resistors encircling one of said waveguide sections, said resistors being connected in parallel with each other and said source and being so poled that current flows therethrough in the same direction, a contact member affixed to the other of said waveguide sections and slidably engaging one or the other of said pair of resistors at a point determined by the relative angular adjustment of said waveguide sections, and circuit means connecting said coil between said contact and a terminal of said direct current source.

6. A microwave rotatable joint adapted to be energized by microwave energy in the TE11 mode comprising, a pair of circular waveguide sections interconnected by a rotatable joint, an elongated member active in the Faraday magnetoaoptical sense positioned interiorly of one of said waveguide sections, an electromagnetic coil positioned to impress a magnetic field on said member longitudinally thereof, a direct current source, a pair of semicircular resistors encircling one of said waveguide sections, said resistors being connected in parallel with each other and said source and being so poled that current flows therethrough in the same direction, a contact member afiixed to the other of said waveguide sections and slidably engaging one or the other of said pair of resistors at .a point determined by the relative angular adjustment of said waveguide sections, and circuit means connecting said coil between said contact and an intermediate terminal of said direct current source.

7. A microwave rotatable joint comprising, a first circular waveguide section, a second circular waveguide section, a rotatable joint connecting said first and second circular waveguide sections, means for passing microwave field energy in the dominant TEu mode through said circular waveguide sections, a rod of comminuted material active in the Faraday magneto-optical sense positioned coaxially within said first circular waveguide section, an electromagnetic coil positioned coaxially with said first circular waveguide section to apply a magnetic field to said rod, a resistor surrounding one of said waveguide sections, brush means anchored on the other of said waveguide sections in slidable contact with said resistor, said brush means being positionable on said resistor in accordance with the angular position of one waveguide section relative to the other waveguide section, a direct current source connected to energize said resistor, and circuit means interconnecting said coil and said brush means for varying the potential impressed thereon as a function of the position of said brush means on said resistor.

8. A microwave rotatable joint comprising, a first circular waveguide section, a second circular waveguide section, a rotatable joint connecting said first and second circular waveguide sections, means for passing microwave field energy in the dominant TE11 mode through said circular waveguide sections, a rod of comminuted material active in the Faraday magneto-optical sense positioned coaxially within said first circular waveguide section, an electromagnetic coil coaxially associated with said first circular waveguide section to apply a magnetic field to said rod, a continuous annular resistor surrounding one of said waveguide sections, a pair of brushes an chored on the other of said waveguide sections slidably engaging said resistor at diametrically opposed points, said points of engagement being determined by the angular position of one section relative to the other section, a direct current source connected to diametrically opposed terminals on said resistor, and a circuit connecting opposite end terminals of said coil to respective ones of said pair of brushes.

9. A microwave rotatable joint adapted to be energized by microwave energy in the TEn mode comprising, a pair of circular waveguide sections interconnected by a rotatable joint, a rod of comminuted material active in the Faraday magneto-optical sense positioned coaxial-1y within one of said waveguide sections, an electromagnetic coil surrounding said one waveguide section to apply a magnetic field to said rod, a direct current source, a pair of semicircular resistors encircling one of said Waveguide sections, said resistors being connected in parallel With each other and said source, a contact member affixed to the other of said waveguide sections and slidably engaging one or the other of said pair of resistors at a point determined by the relative angular adjustment of said waveguide sections, and circuit means connecting said coil between said contact member and a terminal of said direct current source.

10. A microwave rotatable joint comprising, a first circular waveguide section, a second circular Waveguide section, a rotatable joint connecting said first and second circular waveguide sections, means for passing microwave field energy in the dominant TEu mode through said circular waveguide sections, a rod of comminuted material active in the Faraday magneto-optical sense positioned coaxially within said first circular Waveguide section, an electromagnetic coil coaxially associated with said first circular waveguide section to apply a magnetic fie ld to said rod, 21 pair of semicircular resistors encircling one of said Waveguide sections, a direct current source connected to energize said pair of semicircular resistors in parallel, the currents therein circulating in the same direction, a brush anchored on the other of said waveguide sections in slidable contact with one of the other of said pair of semicircular resistors at a point determined by the relative angular adjustment of said waveguide sections, a circuit connecting one terminal of said coil to said brush, and a circuit connecting the other terminal of said coil to one terminal of said direct current source for energization of the coil to rotate the polarization of said microwave field energy in sense and amount corresponding to the angular position of one said waveguide section relative to said other waveguide section.

11. A microwave rotatable joint adapted to be energized by microwave energy in the TE11 mode comprising, a pair of circular Waveguide sections interconnected by a rotatable joint, a rod of comminuted material active in the Faraday magneto-optical sense positioned coaxially Within one of said waveguide sections, an electromagnetic coil surrounding said one waveguide section to apply a magnetic field to said rod, a direct current source, a pair of semicircular resistors encircling one of said waveguide sections, said resistors being connected in parallel with each other and said source and being so poled that current flows therethrough in the same direction, a contact member affixed to the other of said Waveguide sections and slidably engaging one or the other of said pair of resistors at a point determined by the relative angular adjustment of said Waveguide sections, and circuit means connecting said coil between said contact member and an intermediate terminal of said direct current source.

References Cited in the file of this patent UNITED STATES PATENTS 2,257,783 Bowen Oct. 7, 1941 2,529,381 Frear Nov. 7, 1950 2,546,840 Tyrrell Mar. 27, 1951 2,644,930 Luhrs July 7, 1953 2,748,353 Hogan May 29, 1956 

